Transparent glass-ceramic articles, glass-ceramic precursor glasses and methods for forming the same

ABSTRACT

Embodiments of glass ceramic articles and precursor glasses are disclosed. In one or more embodiments, the glass-ceramic articles are transparent and include a nepheline phase and a phosphate phase. The glass-ceramic articles are colorless and exhibit a transmittance of about 70% or greater across the visible spectrum. The glass-ceramic articles may optionally include a lithium aluminosilicate phase. The crystals of the glass-ceramic articles may have a major cross-section of about 100 nm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application and claims the benefit ofpriority under 35 U.S.C. §120 of U.S. application Ser. No. 14/707,127,filed on May 8, 2015, issued as U.S. Pat. No. 9,359,243 on Jun. 7, 2016,which claims the benefit of priority under 35 U.S.C. §119 of U.S.Provisional Application Ser. No. 62/003,636 filed on May 28, 2014, andU.S. Provisional Application Ser. No. 61/992,490 filed on May 13, 2014,the contents of which are relied upon and incorporated herein byreference in their entirety.

BACKGROUND

The disclosure relates to transparent glass-ceramic articles withimproved mechanical strength, and precursor glasses and methods used toform such glass-ceramic articles, and more particularly to transparentglass-ceramic articles that include a nepheline crystalline phase and atransmittance of about 70% or greater, along the visible spectrum.

Sodium aluminosilicate glasses can be strengthened by ion exchangeprocesses in which sodium cations present in the glasses are exchangefor larger, potassium cations. Opaque nepheline-containingglass-ceramics can also be strengthened in the same manner.

Nepheline-containing glass-ceramics are typically nucleated by using aTiO₂ nucleating agent. A significant amount of TiO₂ nucleating agent istypically required to produce internal nucleation innepheline-containing glass-ceramics (e.g., from about 5-10 wt %), whichis an amount sufficient to cause a yellow or amber color in the parentglass (from which the glass-ceramic article is formed).

Accordingly, there is a need for transparent, colorlessnepheline-containing glass-ceramic articles that exhibit improvedmechanical strength and can be strengthened by known ion exchangemethods.

SUMMARY

A first aspect of this disclosure pertains to transparent and highlycrystalline nanophase glass-ceramic articles that exhibit improvedmechanical strength. In one or more embodiments, the glass-ceramicarticles exhibit such improved mechanical strength by exhibiting a highsurface compressive stress that may be achieved or generated byexchanging potassium cations for sodium cations present in theglass-ceramic articles. In one or more embodiments, the glass-ceramicarticles include a principal or major phase including nepheline. Thenepheline phase may include a solid solution. In some embodiments, theglass-ceramic articles include a phosphate phase, which may be presentas a minor phase (in comparison to the nepheline phase) and an optionallithium aluminosilicate (“LAS”) phase, which may be present as a minorphase (in comparison to the nepheline phase).

In some embodiments, at least one of the nepheline phase and thephosphate phase includes a plurality of nanocrystals having a majorcross-sectional dimension of about 100 nm or less. In some instances, aplurality of nanocrystals form at least one of the nepheline phase, thephosphate phase and the lithium aluminosilicate phase, and suchplurality of nanocrystals have a major cross-sectional dimension ofabout 100 nm or less. In some embodiments, the plurality of nanocrystalshaving a major cross-sectional dimension of about 100 nm or less formall three of the nepheline phase, the phosphate phase and the lithiumaluminosilicate phase, when present in the glass-ceramic articles.

In one or more embodiments, the glass-ceramic article is colorless andexhibits a transmittance of about 70% or greater across the visiblespectrum, in the range from about 390 nm to about 700 nm.

In one or more embodiments, the glass-ceramic article includes acomposition, in mol %, including: SiO₂ in the range from about 35 toabout 60, Al₂O₃ in the range from about 10 to about 30, Na₂O in therange from about 7 to about 31, K₂O in the range from about 0 to about20, Li₂O in the range from about 0 to about 20, P₂O₅ in the range fromabout 1.5 to about 8, and a rare earth oxide in the range from about 0to about 6. In some specific embodiments, the composition may include:SiO₂ in the range from about 40 to about 55, Al₂O₃ in the range fromabout 14 to about 21, Na₂O in the range from about 13 to about 29, K₂Oin the range from about 2 to about 14, Li₂O in the range from about 0 toabout 10, P₂O5 in the range from about 2.5 to about 5, and at least oneof ZrO₂, Y₂O₃ and La₂O₃ in an amount in the range from about 0 to about4.

In some embodiments, the composition of the glass-ceramic article canoptionally include at least one oxide in an amount in the range from 0mol % to about 8 mol %. Exemplary oxides include B₂O₃, MgO, CaO, SrO,BaO, and ZrO₂. The composition of the glass-ceramic article (and theprecursor glass used to form the glass-ceramic article) may include lessthan about 1 mol % TiO₂.

The glass-ceramic of one or more embodiments may include a kalsilitephase. In some embodiments, the glass-ceramic article may include acompressive stress layer, the compressive stress layer that optionallyincludes kalsilite. This kalsilite phase may be generated by an ionexchange process, by which the compressive stress layer is formed. Insome embodiments, the glass-ceramic article may have an average surfacecompressive stress of about 400 MPa or greater (e.g., in the range fromabout 400 MPa to about 2 GPa).

A second aspect of the present disclosure pertains to a method forforming a glass ceramic article. The method of one or more embodimentsincludes heat treating a precursor glass article by heating theprecursor glass article at a rate in the range from about 1° C./minuteto about 10° C./minute to produce a glass-ceramic article having anepheline phase and cooling the glass-ceramic article to about roomtemperature. In one or more embodiments, heating the precursor-glass mayinclude a single heating step to a temperature in the range from about600° to about 1000° C. or from about 725° C. to about 900° C. In someinstances, heating the precursor glass may include more than one heattreatment. For example, in some embodiments, heating the precursor glassmay include any one or more of the following: a) heating the precursorglass, which may be nucleated, at a rate in the range from about 1°C./minute to about 10° C./minute to a crystallization temperature (Tc)in the range from about 600° to about 900° C. (or more specifically fromabout 700° C. to about 850° C.), and b) maintaining the precursor glass,which may be nucleated, article at the Tc. At Tc of greater than about900° C., the resulting glass-ceramic may be translucent or opaque.Optionally, prior to heating the precursor glass to Tc, the method mayinclude heating the precursor glass to a temperature (Tn) in the rangefrom about 700° C. to about 900° C., and maintaining the precursor glassarticle at the Tn to produce a nucleated precursor glass article. Insome embodiments, maintaining the precursor glass article to the Tn toproduce a nucleated precursor glass article may be omitted.

In one or more embodiments, the method includes ion exchanging theglass-ceramic article to generate a compressive stress layer comprisinga compressive stress of at least 400 MPa. In some embodiments, themethod includes ion exchanging the glass-ceramic article to generate akalsilite surface layer. In some embodiments, the method includes ionexchanging the glass-ceramic by exposing the glass-ceramic article to amolten salt bath having a temperature of less than about 400° C. In someother embodiments, the method includes ion exchanging the glass-ceramicby comprises exposing the glass-ceramic article to a molten salt bathhaving a temperature of about 400° C. or greater. In such embodiments inwhich a higher temperature molten salt bath is utilized, the resultingglass-ceramic article has a transmittance of about 70% or greater,across the visible spectrum, and includes a surface compressive stressof about 900 MPa or greater.

The precursor glass article may be a glass sheet, though other shapesare contemplated. In one or more embodiments, the glass sheet may beformed by a rolling process in which the glass sheet has a thickness ofabout less than 5 mm. The glass sheet may be formed by other methodslike float processes, spinning processes or even pressing processes(e.g., for relatively small pieces with a sufficient thickness).

Another aspect of this disclosure pertains to a precursor glasscomprising a composition, in mol %, comprising: SiO₂ in the range fromabout 35 to about 60, Al₂O₃ in the range from about 10 to about 30, Na₂Oin the range from about 7 to about 31, K₂O in the range from about 0 toabout 20, Li₂O in the range from about 0 to about 20, P₂O₅ in the rangefrom about 1.5 to about 8, and a rare earth oxide in the range fromabout 0 to about 6. The precursor glass may include at least one oxidein an amount in the range from 0 mol % to about 8 mol %, wherein the atleast one oxide comprises one of B₂O₃, MgO, CaO, SrO, BaO, and ZrO₂. Insome embodiments, the precursor glass includes a composition, in mol %,including SiO₂ in the range from about 40 to about 55, Al₂O₃ in therange from about 14 to about 21, Na₂O in the range from about 13 toabout 29, K₂O in the range from about 2 to about 14, Li₂O in the rangefrom about 0 to about 10, P₂O5 in the range from about 2.5 to about 5,and at least one of ZrO₂, Y₂O₃ and La₂O₃ in an amount in the range fromabout 0 to about 4. In some embodiments, the precursor glass compositionincludes less than about 1 mol % TiO₂.

The precursor glass may include a compressive stress layer having asurface compressive stress in the range from about 200 MPa to about 1000MPa and a depth of layer in the range from about 50 μm to about 150 μm.

Another aspect of this disclosure pertains to forming a glass article.In one or more embodiments, the method includes providing a glasscomposition as described herein, forming a glass article from thecomposition, and ion exchanging the glass article to generate acompressive stress layer comprising a compressive stress of at least 200MPa and a depth of layer in the range from about 50 μm to about 150 μm.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the concentration of K₂O as a function ofdepth within a glass-ceramic formed from the precursor glass of Example5, before and after ion exchanging, as measured by EMPA;

FIG. 2 is a graph showing the compressive stress profiles as a functionof depth of glass-ceramics formed from the precursor glass of Example 5,after being ion exchanged;

FIG. 3 is a graph showing K₂O concentration as a function of depth ofthe glass-ceramics formed from the precursor glass of Example 5;

FIG. 4A is a graph showing the total transmission and diffusetransmission of a glass-ceramic formed from the precursor glass ofExample 5, prior to being ion exchanged;

FIG. 4B is a graph showing the total transmission and diffusiontransmission of the glass-ceramic shown in FIG. 4B after being ionexchanged; and

FIG. 5 is a graph showing the ln(T_(total))/1 mm thickness as a functionof 1/λ⁴ for the precursor glass of Example 5 after being ion exchangedand glass-ceramics formed therefrom before and after being ionexchanged.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings.

A first aspect of this disclosure pertains to glass-ceramic articles andthe precursor glasses used to form such articles. In one or moreembodiments, the glass-ceramic article is transparent and exhibitssuperior mechanical strength. The glass-ceramic article of one or moreembodiments includes one or more crystalline phases such as a nephelinephase and a phosphate crystalline phase. In some embodiments, thenepheline phase is the primary or major phase, while the phosphatecrystalline phase comprises a minor phase. There may be more than oneminor phase present in some embodiments. For example, the glass-ceramicarticles may include a minor phase of LAS.

In one or more embodiments, the nepheline phase may be present as asolid solution (ss), and may optionally have a hexagonal structure.Exemplary compositions of the nepheline phase include NaAlSiO₄,NaAlSiO₄—SiO₂ solid solution, (Na,K)AlSiO₄ solid solution, and/or(Na,K)AlSiO₄—SiO₂) solid solution, where Na predominates over K. In someinstances, the nepheline solid solution minerals are hexagonal (P6₃)tectosilicates whose structures are “stuffed” derivatives of theβ-tridymite form of silica. The general formula of such hexagonal (P6₃)tectosilicates is R(Al,Si,B)O₄, where R=Na,K,Ca or a vacancy. Theformula may be given in terms of solid solution end members:Ne_(x)Ks_(y)An_(z)Q_(1-x-y-z), where Ne=NaAlSiO₄ (soda nepheline),Ks=KAlSiO₄ (kalsilite), An=CaAl₂Si₂O₈ (anorthite) and Q=SiO₂ (quartz).In some embodiments, some CaO may be present. In one or more specificembodiments, the nepheline compositions may include (K,Na)SiO₄, as aprimary component in some instances, with some excess SiO₂.

In one or more embodiments, the glass-ceramic articles include aphosphate crystal phase, which may form a minor phase, in relation tothe nepheline phase. In some instances, the phosphate crystals may beformed at lower temperatures than the nepheline crystals. In someembodiments, the phosphate crystals may nucleate the crystallization ofnepheline on a fine scale (e.g., a scale of about tens of nanometers).These phosphate nucleant crystals, which may be preceded during heattreatment by an amorphous phase separation, have been found by x-raydiffraction to include orthophosphates. Exemplary orthophosphatesinclude Na₃PO4, or (Na,K)₃PO₄, NaBaPO₄, NaCaPO₄ (rhenanite), Li₃PO₄(lithiophosphete), YPO₄ (xenotime), LaPO₄ (monazite), RE(PO₄), NaMgPO₄,NaSrPO₄, NaBaPO₄, and combinations thereof. In embodiments in which theprecursor glass used to form the glass-ceramic articles includes Li₂O(either in addition to or instead of Na₂O), lithiophosphate (Li₃PO₄) maybe present. In other embodiments, when Y₂O₃, La₂O₃ and/or RE₂O₃ (RE=rareearths) are included in the precursor glass used to form theglass-ceramic articles, orthophosphates of these elements are present inthe resulting glass-ceramic articles. In some embodiments, thenucleation of the nepheline phase by these orthophosphates results inthe formation of crystals having a major dimension in the range fromabout 25 nm to about 35 nm, which enhances the transparency of theglass-ceramic articles. In some instances, the transparency of theresulting glass-ceramic article may be such that the glass-ceramicarticle is indistinguishable by the naked eye, from the precursor glassused to form the glass-ceramic articles.

The crystalline phases of the glass-ceramic articles may be formed usingP₂O₅ as a nucleating agent. In some embodiments, the P₂O₅ is added orincluded in a precursor glass in an amount at or near the nepheline ssstoichiometries as listed above. As will be described in greater detailherein, heat treating such precursor glasses can yield clear, colorlessand highly crystalline transparent glass-ceramic articles with thenepheline and phosphate crystal phases described herein. As used herein,the term “colorless” means transmission or reflection color coordinatesunder the CIE L*, a*, b* colorimetry system in the following ranges: L*in the range from about 80 to about 100 (e.g., from about 85 to 100,from about 90 to 100, or from about 95 to 100), a* in the range fromabout −5 to about 5 (e.g., from about −3 to 3, from about −2 to 2, orfrom about −1 to 1), and b* in the range from about b* in the range fromabout −5 to about 5 (e.g., from about −3 to 3, from about −2 to 2, orfrom about −1 to 1).

In one or more embodiments, the glass-ceramic articles may include aminor phase of kalsilite, which may be formed upon heat treating. Theinclusion of a minor kalsilite crystal phase does not alter thetransparency of the resulting glass-ceramic. As will be discussed ingreater detail below, the presence of kalsilite may improve themechanical strength (e.g., in terms of surface compressive stress) ofthe glass-ceramic articles.

In one or more embodiments, the relative amounts of the crystallinephases described herein can be modified to provide desirable properties.For example, as nepheline typically has a high coefficient of thermalexpansion (e.g., greater than about 10×10⁻⁶K⁻¹). The addition of a LASphase having a lower coefficient of thermal expansion, accompanying thenepheline and orthophosphate phases may be useful in increasing thermalshock resistance of the glass-ceramic articles. An example of an LASphase includes gamma (γ) eucryptite.

In one or more embodiments, the glass-ceramic articles exhibit a hightransmittance and low reflectance, even at thicknesses up to about 10 mm(e.g., 0.1 mm to about 10 mm, 0.3 mm to about 10 mm, 0.4 mm to about 10mm, 0.5 mm to about 10 mm, or 1 mm to about 10 mm) As used herein, theterm “transmittance” is defined as the percentage of incident opticalpower within a given wavelength range transmitted through a material(e.g., the glass-ceramic article, or the precursor glasses). The term“reflectance” is similarly defined as the percentage of incident opticalpower within a given wavelength range that is reflected from a material(e.g., the article, the substrate, or the optical film or portionsthereof). Transmittance and reflectance are measured using a specificlinewidth. In one or more embodiments, the spectral resolution of thecharacterization of the transmittance and reflectance is less than 5 nmor 0.02 eV. The transmittance and/or reflectance values provided hereinare across the visible spectrum. As used herein, the visible spectrumincludes wavelengths in the range from about 390 nm to about 700 nm.

The glass-ceramic articles of one or more embodiments may exhibit atransmittance in the range from about 50% to about 93%. In someembodiments, the transmittance may be in the range from about 55% toabout 93%, from about 60% to about 93%, from about 65% to about 93%,from about 70% to about 93%, from about 75% to about 93%, from about 85%to about 93%, from about 90% to about 93%, from about 50% to about 90%,from about 50% to about 85%, from about 50% to about 80%, from about 50%to about 75%, from about 50% to about 70%, from about 90% to about 93%,or from about 90% to about 92%, and all ranges and sub-rangestherebetween.

In one or more embodiments, the glass-ceramic articles may exhibit areflectance of about 10% or less as measured on both surfaces. In someinstances, the reflectance may be about 9% or less, about 8% or less, orabout 7% or less.

The glass-ceramic articles of one or more embodiments may exhibit a lowhaze and/or transmission haze. In some instances, “haze” and“transmission haze” refer to the percentage of transmitted lightscattered outside an angular cone of ±4.0° in accordance with ASTMprocedure D1003, the contents of which are incorporated herein byreference in their entirety as if fully set forth below. In one or moreembodiments, the glass-ceramic articles may have a haze of about 5% orless, or more specifically, about 1% or less.

The sizes of the crystals in the glass-ceramic articles are tailored toprovide the improved mechanical strength and/or optical performance(e.g., transparency). In one or more embodiments, the crystalline phasesmay be described as nanophase such that the crystals in the crystallinephases have a major dimension of about 100 nm or less. In someinstances, the crystals have a major dimension of about 90 nm or less,about 80 nm or less, about 70 nm or less, about 60 nm or less, about 50nm or less, about 40 nm or less, about 30 nm or less, or about 20 nm orless. In some embodiments, about 50% or more of the crystals in any oneor more of the crystalline phases (e.g., nepheline phase, phosphatecrystal phase, and/or LAS phase) have the major dimensions describedherein. For example, about 50%, 60%, 70%, 80%, 90%, 95% or 100% of thecrystals in any one or more of the crystalline phases have a majordimension of about 100 nm or less. In some instances about 95% or 100%of the crystals of any one or more crystalline phases have a majordimension of about 50 nm or less. For example, all the crystals in aglass-ceramic article may have major dimensions of 100 nm or less. Insome embodiments, the crystal sizes of the one or more crystallinephases may be modified, while taking into consideration the desiredrefractive index of a glass-ceramic article. For example, the foregoingcrystal sizes may be suitable to provide high transparency and low lightscattering, where the resulting glass-ceramic article has a refractiveindex in the range from about 1.3 to about 1.7.

In some embodiments, the glass-ceramic articles may be described ashighly crystalline. In such embodiments, the crystalline phase(s) mayinclude about 50% by weight or greater of the glass-ceramic article. Insome instances, the crystalline phase(s) may include about 50 wt % toabout 100 wt % of a glass-ceramic article. In some embodiments, thecrystalline phase(s) may include about 60 wt % to about 100 wt %, about70 wt % to about 100 wt %, about 80 wt % to about 100 wt %, or about 85wt % to about 90 wt %, of a glass-ceramic article.

The glass-ceramic articles described herein and the precursor glassesused to form such articles may include a composition, in mol %,including: SiO₂ in the range from about 35 to about 60, Al₂O₃ in therange from about 10 to about 30, Na₂O in the range from about 7 to about31, K₂O in the range from about 0 to about 20, Li₂O in the range fromabout 0 to about 20, P₂O₅ in the range from about 1.5 to about 8, and arare earth oxide in the range from about 0 to about 6. In one or moreembodiments, the composition may include one or more oxides such asB₂O₃, MgO, CaO, SrO, BaO, and ZrO₂, in an amount in the range from 0 mol% to about 8 mol %.

In one or more embodiments, the amount of SiO₂ in the compositions ofthe precursor glasses and/or glass-ceramics articles may be, in mol %,in the range from about 35 to about 60, from about 35 to about 58, fromabout 35 to about 56, from about 35 to about 55, from about 35 to about54, from about 35 to about 52, from about 35 to about 50, from about 35to about 45, from about 36 to about 60, from about 38 to about 60, fromabout 40 to about 60, from about 42 to about 60, from about 44 to about60, from about 45 to about 60, from about 40 to about 55, from about 45to about 55, from about 45 to about 50, from about 50 to about 60, orfrom about 47 to about 53, and all ranges and sub-ranges therebetween.SiO₂ can be the main constituent of the composition and, as such, canconstitute a matrix of the glass in the precursor glass and/or theglass-ceramic. Also, SiO₂ can serve as a viscosity enhancer for aidingin the formability of a glass, while imparting chemical durability tothe glass.

In some embodiments, the amount of Al₂O₃ in the compositions of theprecursor glasses and/or glass-ceramics may be, in mol %, in the rangefrom about 10 to about 30, from about 12 to about 30, from about 14 toabout 30, from about 16 to about 30, from about 18 to about 30, fromabout 20 to about 30, from about 10 to about 28, from about 10 to about26, from about 10 to about 25, from about 10 to about 24, from about 10to about 22, from about 10 to about 20, from about 10 to about 15, fromabout 14 to about 25, from about 14 to about 21, from about 15 to about25, or from about 16 to about 24, from about 17 to about 23, or fromabout 18 to about 22, and all ranges and sub-ranges therebetween.

In some embodiments, Na₂O may be present in the compositions of theprecursor glasses and/or glass-ceramics, in mol %, in the range fromabout 7 to about 31, from about 7 to about 30, from about 7 to about 28,from about 7 to about 26, from about 7 to about 24, from about 7 toabout 22, from about 7 to about 20, from about 8 to about 31, from about10 to about 31, from about 12 to about 31, from about 13 to about 31,from about 13 to about 29, from about 13 to about 25, or from about 13to about 24, and all ranges and sub-ranges therebetween.

In some embodiments, K₂O may be present in the compositions of theprecursor glasses and/or glass-ceramics, in mol %, in the range fromabout 0 to about 20, from about 0 to about 18, from about 0 to about 16,from about 0 to about 14, from about 0 to about 12, from about 0.1 toabout 20, from about 0.1 to about 18, from about 0.1 to about 16, fromabout 0.1 to about 14, from about 0.1 to about 12, 2 to about 20, fromabout 4 to about 20, from about 6 to about 20, from about 8 to about 20,from about 10 to about 20, from about 2 to about 18, from about 2 toabout 16, from about 2 to about 12, or from about 2 to about 10, and allranges and sub-ranges therebetween.

In some embodiments, Li₂O may be present in the compositions of theprecursor glasses and/or glass-ceramics, in mol %, in the range fromabout 0 to about 20, from about 0 to about 18, from about 0 to about 16,from about 0 to about 14, from about 0 to about 12, from about 0 toabout 10, from about 0.1 to about 20, from about 0.1 to about 18, fromabout 0.1 to about 16, from about 0.1 to about 14, from about 0.1 toabout 12, from about 0.1 to about 10, from about 2 to about 20, fromabout 4 to about 20, from about 6 to about 20, from about 8 to about 20,from about 10 to about 20, from about 2 to about 18, from about 2 toabout 16, from about 2 to about 12, or from about 2 to about 10, and allranges and sub-ranges therebetween.

In some embodiments, the precursor glasses and/or glass-ceramics mayhave a composition including, in mol %, one or more rare earth oxidessuch as Y₂O₃ and La₂O₃. In one or more embodiments, such oxides arepresent, in mol %, in the range from about 0 to about 6, from about 0 toabout 5, from about 0 to about 4, from about 0 to about 3, from about 0to about 2, from about 0 to about 1, from about 0.1 to about 6, fromabout 0.1 to about 5, from about 0.1 to about 4, from about 0.1 to about3, from about 0.1 to about 2, or from about 0.1 to about 1, and allranges and sub-ranges therebetween.

In some embodiments, the precursor glasses and/or glass-ceramics mayhave a composition including one or more oxides selected from any one ofB₂O₃, MgO, CaO, SrO, BaO, and ZrO₂. Any one or more of such oxides maybe present, in mol %, in an amount in the range from about 0 to about 8,from about 0 to about 6, from about 0 to about 5, from about 0 to about4, from about 0 to about 3, from about 0 to about 2, from about 0 toabout 1, from about 0.1 to about 8, from about 0.1 to about 6, fromabout 0.1 to about 5, from about 0.1 to about 4, from about 0.1 to about3, from about 0.1 to about 2, or from about 0.1 to about 1, and allranges and sub-ranges therebetween.

The compositions of the precursor glass and/or glass-ceramics may alsoinclude one or more nucleating agents. The one or more nucleation agentsare incorporated to facilitate nucleation and/or growth of at leastcrystalline phase and any desired one or more minor crystalline phasesduring thermal treatment (e.g., nucleation and/or crystallization) ofthe precursor glasses described herein.

In some embodiments, the one or more nucleating agents may include P₂O₅and/or ZrO₂. P₂O₅ may be present in the compositions of the precursorglass and/or glass-ceramics in an amount from about 1.5 to about 8, fromabout 2 to about 8, from about 2.5 to about 8, from about 3 to about 8,from about 3.5 to about 8, from about 1.5 to about 7.5, from about 1.5to about 7, from about 1.5 to about 6.5, from about 1.5 to about 6, fromabout 1.5 to about 5.5, from about 1.5 to about 5, from about 2.5 toabout 6, from about 2.5 to about 5, or from about 2.2 to about 4, andall ranges and sub-ranges therebetween. ZrO₂ can be included in thecompositions of the precursor glass and/or glass ceramics in an amountfrom about 0 to about 6, from about 0 to about 5, from about 0 to about4, from about 0 to about 3, from about 0 to about 2, from about 0 toabout 1, from about 0.1 to about 6, from about 0.1 to about 5, fromabout 0.1 to about 4, from about 0.1 to about 3, from about 0.1 to about2, or from about 0.1 to about 1, and all ranges and sub-rangestherebetween.

In one or more embodiments, the compositions of the precursor glassesand/or glass-ceramic articles include about 1 mol % or less of TiO₂. Insome embodiments, the amount of TiO₂ is limited to about 0.5 mol % orless. In some instances, the compositions of the precursor glassesand/or glass-ceramic articles are substantially free of TiO₂. As usedhere, the phrase “substantially free” means that a component is notpurposely included in the composition and any amounts present are traceamounts limited to about 0.01 mol % or less.

In some embodiments, Ce, Fe and/or Sn may be included in the compositionof the precursor glass and/or glass-ceramic articles as part of a finingpackage during glass formation. Other fining agents can also be used,such as chlorides and/or sulfates.

The glass-ceramic articles and precursor glasses used to form sucharticles may include a compressive stress layer extending from thesurface of the glass-ceramic article and/or precursor glass to a depthwithin the glass-ceramic article and/or precursor glass. As will bedescribed in greater detail below, such compressive stress layers may beformed or introduced into the glass-ceramic articles and/or precursorglasses through various processes. One such process includes an ionexchange process by which the precursor glass and/or glass-ceramicarticles are immersed or exposed to an ion exchange bath having aspecific composition and temperature, for a specified time period, toimpart to the one or more surfaces with compressive stress(es) (σs). Thecompressive stresses can include one or more average surface compressivestress (CS), and/or one or more depths of compressive stresses (whichmay be referred to as one or more depths of layer (DOL)).

The compressive stress (σ_(s)) of the surface compressive stress layer,average surface compression (CS) of the glass-ceramics and precursorglasses described herein can be conveniently measured using conventionaloptical techniques and instrumentation such as commercially availablesurface stress meter models FSM-30, FSM-60, FSM-6000LE, FSM-7000H . . .etc. available from Luceo Co., Ltd. and/or Orihara Industrial Co., Ltd.,both in Tokyo, Japan. In some instances, additional analysis may berequired to determine an accurate stress profile. For example, inembodiments in which kalsilite is present, addition analysis may berequired. CS, DOL and the stress profile may be measured by refractednear-field (RNF), as more fully described in U.S. Pat. No. 8,854,623.

The precursor glasses and glass-ceramic articles described herein mayhave the same or overlapping compressive stress profiles (includingaverage surface compressive stress values and/or DOLs). In some otherinstances, the precursor glasses and glass-ceramic articles may exhibitdiffering compressive stress profiles.

In one or more embodiments, the precursor glasses (prior to being heattreated) may exhibit an average surface compressive stress of up toabout 1200 MPa. In some instances, the average surface compressivestress is in the range from about 200 MPa to about 1200 MPa. In somespecific instances, the average surface compressive stress may be in therange from about 200 MPa to about 500 MPa, from about 200 MPa to about400 MPa, or from about 300 MPa to about 500 MPa, as measured by FSM. Theprecursor glasses of one or more embodiments (prior to being heattreated) may have a DOL of up to about 150 μm. In some instances, theDOL of the precursor glasses may be in the range from about 50 μm toabout 150 μm, from about 60 μm to about 150 μm, from about 70 μm toabout 150 μm, from about 80 μm to about 150 μm, from about 90 μm toabout 150 μm, from about 70 μm to about 120 μm, from about 70 μm toabout 110 μm, from about 70 μm to about 100 μm or from about 70 μm toabout 90 μm, as measured by FSM or comparable methods.

In one or more embodiments, the glass-ceramic articles may exhibit anaverage surface compressive stress of about 200 MPa or greater. In someinstances, the average surface compressive stress is in the range fromabout 200 MPa to about 1600 MPa. In some specific instances, the averagesurface compressive stress may be in the range from about 400 MPa toabout 1600 MPa, from about 600 MPa to about 1600 MPa, from about 700 MPato about 1600 MPa, from about 800 MPa to about 1600 MPa, from about 900MPa to about 1600 MPa, from about 200 MPa to about 1400 MPa, from about400 MPa to about 1400 MPa, from about 600 MPa to about 1400 MPa, fromabout 700 MPa to about 1400 MPa, from about 800 MPa to about 1400 MPa,from about 900 MPa to about 1400 MPa, as measured by FSM. Theglass-ceramic articles of one or more embodiments may have a DOL of upto about 100 μm. In some instances, the DOL of the glass-ceramicarticles may be in the range from about 10 μm to about 100 μm, fromabout 20 μm to about 100 μm, from about 30 μm to about 100 μm, fromabout 40 μm to about 100 μm, from about 50 μm to about 100 μm or fromabout 60 μm to about 100 μm, as measured by FSM.

In some instances, the compressive stress in the glass-ceramic articlesis a result of the exchange of potassium cations into the glass-ceramicarticle and in particular into the nepheline crystals, with sodium or asmaller cation exchanging out of the glass-ceramic article. Thepotassium ions expand the unit cell of the nepheline crystals andincrease compression in the surface of the glass-ceramic article.

In some embodiments, phase transformation from nepheline (Na,K)AlSiO₄ tokalsilite (KAlSiO₄) can also occur, yielding even higher surfacecompression. In one or more embodiments, the glass-ceramic articles mayinclude kalsilite, which may be present in the compressive stress layer,as the sodium cations present in the glass-ceramic articles areexchanged for potassium cations. In one or more embodiments, thepresence of kalsilite, generated through the ion exchange process, inthe compressive stress layer results in increased surface compressivestress (e.g., surface CS of greater than about 1000 MPa). In someembodiments, the kalsilite is present in a portion of the compressivestress layer (e.g., from the surface of the glass-ceramic article to adepth that is less than the DOL). In some embodiments, the kalsilite ispresent as a layer at the surface (i.e., it forms a surface layer) ofthe glass-ceramic article. The glass-ceramic articles described hereincan be strengthened by an ion exchange process to higher levels than canbe achieved in glasses, because greater surface compression results froma combination of crowding of the larger ion within the nepheline crystaland by ion-exchange-induced phase transformation involving partially orcompletely converting nepheline to kalsilite. Moreover, theglass-ceramic has a higher strain point than glass, and therefore highertemperature salt baths may be used to speed up the ion exchange process.In addition, the greater fracture toughness of glass-ceramics (incomparison to glass), allows higher surface compression and internaltension to develop before a level of undesired frangibility is reached.

In some embodiments, the precursor glasses and/or glass-ceramics mayexhibit abraded ring-on-ring (ROR) values up to about 1000 MPa; however,the glass-ceramic may exhibit abraded ROR values up to 3000 MPa, afterabrading with SiC particles at 5 psi. In some embodiments, the abradedring-on-ring values may be in the range from about 400 MPa to about 1000MPa, from about 500 MPa to about 1000 MPa, from about 600 MPa to about1000 MPa, from about 700 MPa to about 1000 MPa or from about 800 MPa toabout 1000 MPa.

In some embodiments, the glass-ceramics may exhibit a crystallinity suchthat (R-3P)/Al is in the range from about 0.5 to about 1.5, from about0.6 to about 1.1 or from about 0.65 to about 1.1.

In one or more embodiments, the precursor glasses and/or glass-ceramicsmay have to a thickness up to about 10 mm. In some instances thethickness may be in the range from about 0.1 mm to about 10 mm, fromabout 0.2 mm to about 10 mm, from about 0.3 mm to about 10 mm, fromabout 0.5 mm to about 10 mm, form about 0.7 mm to about 10 mm, fromabout 1 mm to about 10 mm, from about 0.7 mm to about 5 mm, from about0.7 mm to about 2 mm, or from about 0.7 mm to about 1.3 mm.

The glass-ceramic articles and/or precursor glasses described herein mayinclude a coating which can provide an added functionality. For example,such coatings can include anti-fingerprint coatings, anti-reflectivecoatings, anti-smudge coatings, easy-to-clean coatings, scratchresistant coatings, and the like. Such coatings may be disposed on asurface of the glass-ceramic article by various methods such as chemicalvapor deposition (CVD) (e.g., plasma-enhanced CVD, aerosol-assisted CVD,metal organic CVD, and the like), any of the variants of physical vapordeposition (PVD) (e.g., ion-assisted PVD, pulsed laser deposition,cathodic arc deposition, sputtering, and the like), spray coating,spin-coating, dip-coating, inkjetting, sol-gel processing, or the like.Such processes are known to those skilled in the art to which thisdisclosure pertains.

Various articles may incorporate or utilize the precursor glasses and/orglass-ceramics described herein. For example, covers and/or housingsused in electronic devices might be formed using the precursor glassesand/or glass-ceramics. In still yet other embodiments, the precursorglasses and glass-ceramics might be used in a variety of electronicdevices or portable computing devices, which might be configured forwireless communication, such as, computers and computer accessories,such as, “mice”, keyboards, monitors (e.g., liquid crystal display(LCD), which might be any of cold cathode fluorescent lights(CCFLs-backlit LCD), light emitting diode (LED-backlit LCD) . . . etc.,plasma display panel (PDP) . . . and the like), game controllers,tablets, thumb drives, external drives, whiteboards . . . etc.; personaldigital assistants (PDAs); portable navigation device (PNDs); portableinventory devices (PIDs); entertainment devices and/or centers, devicesand/or center accessories such as, tuners, media players (e.g., record,cassette, disc, solid-state . . . etc.), cable and/or satellitereceivers, keyboards, monitors (e.g., liquid crystal display (LCD),which might be any of cold cathode fluorescent lights (CCFLs-backlitLCD), light emitting diode (LED-backlit LCD) . . . etc, plasma displaypanel (PDP) . . . and the like), game controllers . . . etc.; electronicreader devices or e-readers; mobile or smart phones . . . etc. Asalternative examples, the precursor glasses and glass-ceramics might beused in automotive (consoles, automotive body parts), appliances, andeven architectural applications (e g, sinks, faucets, shower walls,bathtubs, outlet covers, countertops, backsplashes, elevator cabs,etc.), energy production applications (e.g, solar thermal parts).

A second aspect of this disclosure pertains to a method of forming aprecursor glass, a glass-ceramic article or both a precursor glass and aglass ceramic.

The method for forming a precursor glass (formulated to be precursor toglass ceramics described herein) includes melting at a temperature belowabout 1600° C. a mixture of raw materials formulated to produce uponmelting a precursor glass. The method may include any one or more offining and homogenizing the molten mixture of raw materials at atemperature below about 1600° C. to form a precursor glass. Theprecursor glass may be formed using known methods in the art such asrolling, thin rolling, pressing, casting and float processes. In one ormore embodiments, the precursor glass may be shaped into a flat, planarsheet or may be formed into a three-dimensional shape (e.g., by castinginto a mold or other known methods).

In one or more embodiments, the method for forming a glass-ceramicincludes heat treating the precursor glasses described herein at one ormore preselected temperatures for one or more preselected times toinduce crystallization (i.e., nucleation and growth) of one or morecrystalline phases (e.g., having one or more compositions, amounts,morphologies, sizes or size distributions, etc.). The method includescooling the formed glass-ceramics to room temperature. In one or morespecific embodiments, heat treating the precursor glasses can includeheating precursor glasses at a rate of 1-10° C./min to a maximumtemperature, in the range from about 600° C. to about 1000° C. (e.g.,from about 725° C. to about 900° C. or from about 750° C. to about 900°C.). In some embodiments, heat treating the precursor glasses caninclude more than one heat treatment. For example, in some embodiments,heat treating the precursor glasses can include any one or more of: (i)heating precursor glasses at a rate of 1-10° C./min to a nucleationtemperature (Tn) in the range from about 600° C. to about 750° C.; (ii)maintaining the precursor glasses at the nucleation temperature for atime in the range from between about ¼ hr to about 4 hr to producenucleated precursor glasses; (iii) heating the precursor glasses, whichmay be nucleated, at a rate in the range from about 1° C./min to about10° C./min to a crystallization temperature (Tc) in the range from about700° C. to about 1000° C.; and (iv) maintaining the precursor glasses,which may be nucleated, at the crystallization temperature for a time inthe range from about ¼ hr to about 4 hr to produce the glass-ceramicsdescribed herein.

Temperature-temporal profile of heat treatment steps, in addition toprecursor glass compositions, are judiciously prescribed so as toproduce one or more of the following desired attributes: crystallinephase(s) of the glass-ceramics, proportions of one or more predominatecrystalline phases and/or one or more minor crystalline phases andresidual glass, crystal phase assemblages of one or more predominatecrystalline phases and/or one or more minor crystalline phases andresidual glass, and grain sizes or grain size distributions among one ormore predominate crystalline phases and/or one or more minor crystallinephases, which in turn may influence the final integrity, quality, color,and/or transparency, of resultant formed glass-ceramics. In someembodiments, the heat treatment related to nucleating the precursorglass (e.g., steps (i) and (ii)) may be omitted and the precursor glassmay simply be heat treated at a set temperature (at the rates otherwisedisclosed herein) to form the one or more crystalline phases. Forexample, the precursor glasses may be heated at a rate in the range fromabout 1° C./min to about 10° C./min, to 725° C., 750° C., 775° C., 800°C., 825° C., 850° C., 875° C. or 900° C. for a set amount of time (e.g.,up to about 6 hours, up to about 4 hours, or up to about 2 hours).

The resultant glass-ceramic sheets can then be reformed by pressing,blowing, bending, sagging, vacuum forming, or other means into curved orbent pieces of uniform thickness. Reforming can be done before thermallytreating or the forming step can also serve as a thermal treatment stepwhere both forming and thermally treating are performed substantiallysimultaneously. In some embodiments, the forming might precede thetransforming, or the transforming might precede the forming, or thetransforming might occur substantially simultaneously with the forming.

In some embodiments, the method for forming a precursor glass and/or aglass ceramic includes forming a compressive stress layer in theprecursor glass and/or glass ceramic, as described herein. In one ormore embodiments, the method specifically includes ion exchanging theprecursor glass and/or glass ceramic article by subjecting one or moresurfaces of such precursor glass and/or glass ceramic to one or more ionexchange baths, having a specific composition and temperature, for aspecified time period to impart to the one or more surfaces withcompressive stress(es) (σs). The compressive stresses can include one ormore average surface compressive stress (CS), and/or one or more DOLs.

The bath(s) used in the ion exchange process represent an ion sourcehaving one or more ions having an ionic radius larger than the ionicradius of one or more ions present in the precursor glass and/or glassceramic (and, more particularly, the ions present in at least onesurface of the precursor glass and/or glass ceramic). During immersionof the precursor glass and/or glass ceramic into the bath, the ions inthe precursor glass and/or glass ceramic having smaller radii canreplace or be exchanged with ions having larger radii. This exchange maybe facilitated or achieved by controlling the bath and/or precursorglass and/or glass ceramic temperature within a range of temperatures atwhich ion inter-diffusion (e.g., the mobility of the ions from betweenbath and the glass-ceramic) is sufficiently rapid within a reasonabletime (e.g., between about 1 hr. and 64 hrs. or from 4-16 hrs., rangingat between about 300° C. and 500° C. or from 360° C.-460° C.). Also,typically such temperature is below the glass transition temperature(Tg) of any glass of a glass-ceramic. Some exemplary ions that may beexchanged between the bath and the precursor glass and/or glass ceramicinclude sodium (Na⁺), lithium (Li⁺), potassium (K⁺), rubidium (Rb⁺),and/or cesium (Cs⁺) ions. In one scenario, the bath may include sodium(Na⁺), potassium (K⁺), rubidium (Rb⁺), and/or cesium (Cs⁺) ions, whichmay be exchanged for lithium (Li⁺) ions in the precursor glass and/orglass ceramic. Alternatively, ions of potassium (K⁺), rubidium (Rb⁺),and/or cesium (Cs⁺) in the bath can be exchanged for sodium (Na⁺) ionsin the precursor glass and/or glass ceramic. In another scenario, ionsof rubidium (Rb⁺) and/or cesium (Cs⁺) in the bath may be exchanged forpotassium (K⁺) ions in the precursor glass and/or glass ceramic.

Some examples of ion sources include one or more gaseous ion sources,one or more liquid ion sources, and/or one or more solid ion sources.Among one or more liquid ion sources are liquid and liquid solutions,such as, for example molten salts. For example for the aboveion-exchange examples, such molten salts can be one or more alkali metalsalts such as, but not limited to, one or more halides, carbonates,chlorates, nitrates, sulfites, sulfates, or combinations of two or moreof the proceeding. In one example, suitable alkali metal salts caninclude potassium nitrate (KNO₃), sodium nitrate (NaNO₃) and thecombination thereof. It should be noted that in addition to single stepion exchange processes, multiple step ion exchange processes can beutilized to provide a specific CS to the surface of the precursor glassand/or glass ceramic and thus, enhance the performance of a precursorglass and/or glass ceramic. In some embodiments, single step ionexchange processes can be accomplished by exchanging ion (particularlylithium-for-sodium ion exchange) into a surface of the precursor glassand/or glass ceramic by placing a precursor glass and/or glass ceramicarticle in NaNO₃ baths at between about 300° C. and 500° C. for betweenabout 1 hr and 64 hr. In other embodiments, single step ion exchangeprocesses can be accomplished by placing a precursor glass and/or glassceramic article in a mixed potassium/sodium baths at (e.g. a bathincluding about 0.1 wt % to about 25 wt % NaNO3 with the balance beingKNO₃, a 80/20 KNO₃/NaNO₃ bath, a 60/40 KNO₃/NaNO₃ bath, or even a 50/50KNO₃/NaNO₃ bath . . . etc.) at between about 300° C. and 500° C. forbetween about 1 hr and 64 hr. In still other embodiments, two-step ionexchange process can be accomplished by first placing a precursor glassand/or glass ceramic article in a Li-containing salt bath (e.g. themolten salt bath can be a high temperature sulfate salt bath composed ofLi₂SO₄ as a major ingredient, but diluted with Na₂SO₄, K₂SO₄ or Cs₂SO₄in sufficient concentration to create a molten bath) between about 300°C. and 500° C. for between about 1 hr and 64 hr followed by placing theion exchanged precursor glass and/or glass ceramic in a Na-containingsalt bath between about 300° C. and 500° C. for between about 1 hr and64 hr. The first step of the two step ion exchange process functions toreplace the larger sodium ions in at least one surface of the precursorglass and/or glass ceramic with the smaller lithium ions found in theLi-containing salt bath. The second step of the two step ion exchangeprocess functions to exchange Na into at least one surface of theprecursor glass and/or glass ceramic.

Alternative bath compositions that can be used to ion exchange theprecursor glasses and glass ceramics described herein include KCl/K₂SO₄mixtures, having a temperature of 700° C. or greater. The ratio ofKCl/K2SO4 may be from about 60:40 to about 40:60, or more particularly,from 52:48. Such bath composition can be used to form glass ceramicswith kalsilite on the surface, as described herein. These alternativecompositions can be combined with NaNO₃ or KNO₃, which may be used as apoisoning component. The compressive stress profile of such glassceramics can be modified using these alternative bath compositions. Forexample, in some embodiments, the glass ceramics ion exchanged withthese alternative bath compositions may exhibit a “step” compressivestress profile, as a function of depth of layer, such that the CS ismaintained at a high level for a deeper depth from the surface (e.g.,about 40 μm or greater), and then tapers off at even deeper depths. This“step” profile is believed to be caused by the presence of a kalsilitelayer at the surface. For comparison, most known glasses having acompressive stress profile starts at or near its highest compressivestress level at the surface and tapers off or reduces along the depth,consistently. In other embodiments, the glasses and/or glass ceramicsion exchanged with the alternative bath compositions may exhibit aburied CS peak, such that the CS decreases from the surface but thenincreases at a depth from the surface, before decreasing again at deeperdepths.

In one or more specific embodiments, the method includes generating akalsilite surface layer in the glass-ceramic article. In some instances,generating the kalsilite layer may include transforming a portion of thenepheline phase to kalsilite. In some embodiments, generating thekalsilite layer includes immersing the glass-ceramic article into an ionexchange bath having a temperature of about 400° C. or greater (e.g.,about 450° C.). The ion exchange bath can include KNO₃. The resultingglass-ceramic article exhibits a compressive stress of about 900 MPa orgreater and also exhibits a transmittance of about 70% or greater acrossthe visible spectrum.

Various embodiments will be further clarified by the following examples.

EXAMPLES

In the examples, identification of the phase assemblages and/orcrystalline sizes for the precursor glasses and glass-ceramics describedherein was determined or could be determined by XRD analysis techniquesknown to those in the art, using such commercially available equipmentas the model as a PW1830 (Cu Kα radiation) diffractometer manufacturedby Philips, Netherlands. Spectra were typically acquired for 2θ from 5to 80 degrees. Elemental profiles measured for characterizing thesurfaces of the precursor glasses and/or glass-ceramics described hereinwere determined or could be determined by analytical techniques know tothose in the art, such as, electron microprobe analysis (EMPA), x-rayphotoluminescence spectroscopy (XPS), secondary ion mass spectroscopy(SIMS), etc.

Example 1

The following examples illustrate the advantages and features of thisdisclosure and in are no way intended to limit this disclosure thereto

Inasmuch as the sum of the individual constituents totals or veryclosely approximates 100, for all practical purposes the reported valuesmay be deemed to represent mole %. The actual precursor glass batchingredients may comprise any materials, either oxides, or othercompounds, which, when melted together with the other batch components,will be converted into the desired oxide in the proper proportions.

Examples 1-16

The exemplary precursor glasses listed in Table 1 were made in aplatinum crucible using a batch of raw materials formulated to yield2000 g of precursor glass upon melting and refining. Each cruciblecontaining a formulated raw materials batch was placed in a furnacepreheated to a temperature in the range from about 1450° C. to about1650° C., the formulated raw materials batch melted and refined in thisfurnace for 16 hours to produce molten precursor glass that was thencast into rectangular slabs that were annealed for about 6 hours at atemperature in the range from about 600° C. to about 700° C. Theresulting glass slabs were transparent, colorless and contained nocrystals.

In this way, individual slabs of an exemplary precursor glass could thenbe subject to a number of different and/or similar heat treatments byplacing in a static furnace programmed with such different or similartemperature-temporal cycle. Examples of some of the temperature-temporalcycles to which a number of the slabs of the exemplary precursor glasseslisted in Table 1 were subjected are shown in Table 2 and include:

-   -   introducing the precursor glass into a furnace set at between        room temperature and 500° C.;    -   heating the precursor glass at 5° C./minute (min) to a        temperature in the range from about 725° C. to about 900° C., as        shown in Table 2; and    -   cooling to room temperature.

The appearance of the heat treated slabs of precursor glasses followingheat treatment are provided in Table 2. The rectangular slabs ofprecursor glass, after being subjected to heat treatment, exhibitedimproved transparency as compared to before heat treatment.

Also as determined by X-ray diffraction (XRD) analysis, resultantglass-ceramics exhibited a crystal phase assemblage comprising anepheline phase as a predominant crystalline phase and one or more minorphases including various combinations of a phosphate crystal phase aloneor phosphate crystal phase with LAS phase, as also shown in Table 2.

TABLE 1 Composition of precursor glasses 1-16. 1 2 3 4 5 6 7 8 Wt. %SiO₂ 38 40 37.3 44.2 37.1 43.4 37.2 36.3 Al₂O₃ 27.2 24.4 26.7 23.9 26.523.7 26.6 26 Na₂O 18.2 15.5 20 24.1 19.4 25.1 19.7 19.2 Li₂O 0 0 0 0 0 00 0 K₂O 7.5 8 8.2 0 8 0 8.1 7.9 P₂O₅ 9.1 7.1 7.8 7.8 9 7.8 8.4 8.2 B₂O₃0 0 0 0 0 0 0 2.4 BaO 0 5 0 0 0 0 0 0 Y₂O₃ 0 0 0 0 0 0 0 0 ZrO₂ 0 0 0 00 0 0 0 Total 100 100 100 100 100 100 100 100 Mol % SiO₂ 47.3 50.3 46.152 46.2 51.1 46.1 44.9 Al₂O₃ 19.9 18.1 19.4 16.6 19.4 16.4 19.4 19 Na₂O22 18.9 23.9 27.5 23.4 28.6 23.7 23 Li₂O 0 0 0 0 0 0 0 0 K₂O 6 6.4 6.5 06.3 0 6.4 6.2 P₂O₅ 4.8 3.8 4.1 3.9 4.7 3.9 4.4 4.3 B₂O₃ 0 0 0 0 0 0 02.6 BaO 0 2.5 0 0 0 0 0 0 Y₂O₃ 0 0 0 0 0 0 0 0 ZrO₂ 0 0 0 0 0 0 0 0Total 100 100 100 100 100 100 100 100 9 10 11 12 13 14 15 16 Wt. % SiO₂43.9 38.4 40.6 37.9 37.2 45 37.6 41.6 Al₂O₃ 23.7 26.9 23 26.5 26 27.227.4 29.1 Na₂O 22.7 19.9 21.4 17.2 13.2 12.3 11.4 9.7 Li₂O 0 0 0 0 0 3.50 6.1 K₂O 2 8.2 6.2 11.9 17.2 5.7 8 4.3 P₂O₅ 7.7 6.6 8.8 6.5 6.4 6.3 66.3 B₂O₃ 0 0 0 0 0 0 0 0 BaO 0 0 0 0 0 0 0 Y₂O₃ 0 0 0 0 0 0 9.6 0 ZrO₂ 00 0 0 0 0 0 2.9 Total 100 100 100 100 100 100 100 100 Mol % SiO₂ 52 47.149.2 47.1 47.1 52.1 50.2 47.7 Al₂O₃ 16.6 19.4 16.4 19.4 19.4 18.6 21.519.7 Na₂O 26 23.7 25.1 20.7 16.2 13.8 14.7 10.7 Li₂O 0 0 0 0 0 8.2 014.1 K₂O 1.5 6.4 4.8 9.4 13.9 4.2 6.8 3.1 P₂O₅ 3.9 3.4 4.5 3.4 3.4 3.13.4 3.1 B₂O₃ 0 0 0 0 0 0 0 0 BaO 0 0 0 0 0 0 0 0 Y₂O₃ 0 0 0 0 0 0 3.4 0ZrO₂ 0 0 0 0 0 0 0 1.6 Total 100 100 100 100 100 100 100 100

TABLE 2 Temperature-temporal cycles and appearance after select cyclesfor precursor glasses 1-16 1 2 3 4 5 6 7 8 Heat Treatment at T for 4 hrsT = 775° C. Translucent Translucent Transparent Transparent TransparentTransparent Transparent Opal T = 750° C. Transparent TransparentTransparent Transparent Transparent Transparent Transparent Hazy and butcracked cracked T = 825° C. — — — — Transparent Transparent Transparent— T = 900° C. — — — — — — — — T = 725° C. — — — — — — — TransparentCrystalline phases/assemblages Ne Ne Major Ne Major Ne Major Ne Major NeMajor Ne Major Ne Major Major; Na,BaP NaP Minor NaP Minor NaP Minor NaPMinor NaP Minor NaP Minor NaP Minor Minor 9 10 11 12 13 14 15 16 HeatTreatment at T for 4 hrs T = 775° C. Hazy Transparent TransparentTransparent Transparent Transparent* — Transparent T = 750° C.Transparent Transparent Transparent Transparent Transparent — —Transparent T = 825° C. — Transparent — — — Transparent — — T = 900° C.— — — — — — Transparent — T = 725° C. — — — — — — — — Crystallinephases/assemblages Ne Major Ne Major Ne Major Ne Major Ne Major Ne MajorβYP Ne Major NaP Minor NaP Minor NaP Minor NaP Minor Ks Minor LiP MinorNaP Minor NaP minor LAS Minor Ne = nepheline; NaP = Na₃PO₄; Na,BaP =NaBaPO₄; LiP = Li₃PO₄ (lithiophosphate); Ks = KAlSiO₄; YP = YPO₄; LAS =gamma (γ) LiAlSiO₄ *Ex. 14 - after being cerammed, at 775° C. for 4hours, and then ion exchanged in a molten salt bath of KNO3 at 480 C.for 8 Hours exhibited an average MOR of about 2540 MPa.

The precursor glass of Example 5 and glass-ceramics formed therefromwere evaluated further. Specifically, the profile of K₂O concentration(mol %) as a function of depth, of glass ceramics formed from theprecursor glass of Example 5 (after heat treating at T=775° C. for 4hours), before and after ion exchanging in a molten bath of 100% KNO₃having a temperature of 450° C. for two different time periods: 3.5hours (“Sample 5A”) and 7 hours (“Sample 5B”). The K₂O concentrationsfor the glass-ceramics were measured by EMPA and plotted in FIG. 1. InFIG. 1, the dashed line indicates the amount of K₂O in the glass-ceramicprior to being ion exchanged. As shown in FIG. 1, the glass-ceramic thatwas subjected to a longer ion exchange had a greater concentration ofK₂O along a greater depth (e.g., K₂O concentration at a 18 micron depthfor the sample ion exchanged for 7 hours was about twice as much as theK₂O concentration at the same depth of the sample ion exchanged for 3.5hours). As also shown in FIG. 1, the profiles of K₂O concentration werenot error function-like, as found with the precursor glasses after beingion exchanged similarly. A discontinuity in the slope of the K₂Oconcentration was found at about 8 microns and 13 microns for bothsamples ion exchanged for 3.5 hours and for 7 hours. A surface XRDanalysis indicated the presence of kalsilite (as a layer) at the surfaceof the glass-ceramic articles, which is believed to be a conversion ofnepheline to kalsilite. As discussed herein, this conversion of aportion of the nepheline phase to kalsilite provides substantialstrength increase (in terms of increased compressive stress).

As the chemical profile was non-standard (e.g., the K₂O concentrationhad discontinuities), compressive stress curves were extracted based onthat data. The compressive stress profiles, as a function of DOL, forfour samples (“Samples 5C-5F”) made from the precursor glass of Example5 were measured using FSM, and shown in FIG. 2. The four samples wereformed using the same heat treatment schedule as the samples shown inFIG. 1 (i.e., heat treated at 775° C. for 4 hours), and had a thicknessof 1 mm. The four samples were ion exchanged under different conditions,as shown in Table 3.

TABLE 3 Ion Exchange conditions for glass ceramics 5C-5F. Sample BathConcentration Bath Temperature Ion Exchange Time 5C 95 wt % KNO₃ 450° C.3.5 hours   5 wt % NaNO₃ 5D 95 wt % KNO₃ 450° C. 7 hours 5 wt % NaNO₃5E-1 100 wt % KNO₃ 360° C. 2.5 hours   5E-2 100 wt % KNO₃ 360° C. 7hours 5E-3 100 wt % KNO₃ 360° C. 17 hours  5F 100 wt % KNO₃ 450° C. 7hours

Sample 5F, which was ion exchanged for 7 hours in a molten bath of 100%KNO₃ having a temperature of 450° C. exhibited a surface compressivestress of about 1200 MPa, with a non-monotonic compressive stressprofile extending to a DOL that was greater than about 60 um. Theprecursor glass of Example 5 was ion exchanged under the same conditionsas Sample 5F and exhibited a surface CS of about 400 MPa and a DOL thatwas greater than about 100 μm. A molten bath comprised of 95 wt % KNO₃/5wt % NaNO₃ was also used to ion exchange Samples 5C and 5D, whichexhibited surface compressive stresses greater than about 600 MPa and aDOL of about 60 um were found. Sample 5E was ion exchanged at a lowertemperature (e.g., about 360° C.) for 2.5 hours (“Sample 5E-1”), 7 hours(“Sample 5E-2”) and 17 hours (“Sample 5E-3”). The compressive stressprofiles for Samples 5E-1 and 5E-2 are not shown in FIG. 2; however asurface compressive stress of about 1200 MPa and a DOL of about 40 μmwas observed in Sample 5E-3 after ion exchange for 17 hours at 360° C.

The profiles of K₂O concentration (mol %) as a function of depth, asmeasured by EMPA of Samples 5E-1, 5E-2 and 5E-3 after being ionexchanged at 360° C. for 2.5 hours, 7 hours and 17 hours, respectively,are shown in FIG. 3. The K₂O concentration (mol %) profiles as afunction of depth of Samples 5C and 5D are also shown in FIG. 3.

The total and diffuse transmission for Samples 5C-5E was analyzed and isshown in FIGS. 4A (before ion exchange) and 4B (after ion exchange underthe conditions shown in Table 3). The glass-ceramics had a thickness of1 mm. As shown in FIGS. 4A and 4B, transparency is maintained after ionexchanging.

Diffuse transmission provides an estimate of haze. As shown in FIG. 4A,diffuse transmission is low at wavelengths greater than about 450 nmTotal transmission before ion exchange is greater than about 85% acrossthe visible spectrum and between about 92% and 95% at wavelengthsgreater than about 550 nm.

In FIG. 4B, the solid lines indicate total transmission and the dashedlines indicate diffuse transmission after the ion exchange conditionsshown in Table 3. The total transmission after ion exchange improvedover the total transmission of the samples before ion exchange. Thediffuse transmission varied, with Sample 5D exhibiting the lowestdiffuse transmission, indicating a very low level of haze.

FIG. 5 represents ln(T)/1 mm thickness as a function of 1/λ⁴ for Samples5D-5E before ion exchanging and after ion exchanging at differentconditions as shown in Table 3. The data for the glass ceramics wascompared to the precursor glass of Example 5, after being ion exchangedusing the same conditions used to ion exchange Sample 5D. The data shownin FIG. 5 are well fit to a straight line, suggesting that Rayleighscattering is the dominant loss mechanism. Scatter of the glass ceramicsis 3-4 times higher than the precursor glass; this is consistent withthe finding of crystals having a major dimension of about 30 nm. Basedon FIG. 5, the amount of scatter is not dependent on ion-exchangeconditions.

Examples 17-25

The exemplary precursor glasses listed in Table 4 were made in aplatinum crucible using a batch of raw materials formulated to yield2000 g of precursor glass upon melting and refining. Each cruciblecontaining a formulated raw materials batch was placed in a furnacepreheated to a temperature in the range from about 1450° C. to about1650° C., the formulated raw materials batch melted and refined in thisfurnace for 16 hours to produce molten precursor glass that was thencast into rectangular slabs that were annealed for about 6 hours at atemperature in the range from about 600° C. to about 700° C.

The individual slabs were subject to a number of different and/orsimilar heat treatments to form glass-ceramics by placing the slaps in astatic furnace programmed with such different or similartemperature-temporal cycle. The temperature-temporal cycles to which anumber of the slabs of the exemplary precursor glasses listed in Table 4were subjected are shown in Table 5.

The resulting glass-ceramics were analyzed by XRD to identify thenucleant present in the glass before crystallization to nepheline sstook place. The nucleants were orthophosphates including Na₃PO4, NaCaPO₄(rhenanite), and Li₃PO₄ (lithiophosphate), as shown in Table 4.

TABLE 4 Composition of precursor glasses 17-25. Mol % 17 18 19 20 21 2223 24 25 SiO₂ 46.2 47.1 45.9 44.5 44.9 52.1 48.8 44.3 47 Al₂O₃ 19.4 19.419.4 18.7 19 18.6 20.1 18.2 23.5 Na₂O 23.4 23.7 23.3 24.8 23 13.8 7.122.3 17.4 K₂O 6.3 6.4 6.2 7.5 6.2 4.2 2.9 6 5.6 Li₂O 0 0 0 0 0 8.2 16.50 0 P₂O₅ 4.7 3.4 5.2 4.5 4.3 3.1 3.2 3.2 2.5 CaO 0 0 0 0 0 0 0 0 4 B₂O₃0 0 0 0 2.6 0 0 0 0 ZrO₂ 0 0 0 0 0 0 1.4 6 0 Total 100 100 100 100 100100 100 100 100 Nucleant Na₃PO₄ Na₃PO₄ Na₃PO₄ Na₃PO₄ Na₃PO₄ Li₃PO₄Li₃PO₄ Na₃PO₄ NaCaPO₄

It should be noted that in the compositions of Table 4, the effectiveratio of Na/(Na+K), after removing the Na to form the nucleatingphosphate (or phosphate nucleant), may be varied in the range from about0.45 to about 0.9.

TABLE 5 Temperature-temporal cycles for precursor glasses 17-25. 17 1819 20 21 22 23 24 25 Heat Treatment at T for XXhrs T = 775° C. 4 4 4 4 44 T = 750° C. 4 T = 825° C. 4 T = 900° C. T = 725° C. 4 Crystallinephases/assemblages Ne + NaP Ne + NaP Ne + NaP Ne + NaP Ne + NaP Ne + LiPNe + LAS + Ne + NaP + Ne + NaCaPO₄ LiP + lithium ZrO₂ disilicate Ne =nepheline; NaP = Na₃PO₄; Na,BaP = NaBaPO₄; LiP = Li₃PO₄(lithiophosphate); Ks = KAlSiO₄; YP = YPO₄; LAS = gamma (γ) LiAlSiO₄

The glass ceramic of Example 17 exhibited a compressive stress having adeep depth of layer. The glass ceramic of Example 17 also exhibited lowcrystallinity (i.e., (R-3P)/Al=0.80).

The glass-ceramic of Example 18 exhibited stoichiometric, highcrystallinity and (R-3P)/Al=1.0.

The glass-ceramic of Example 19 exhibited the deepest depth of layer andlowest (R-3P)/Al=0.72.

The glass-ceramic of Example 20 exhibited (stoichiometric (R-3P)/Al=1.0)and a higher amount of P₂O₅ relative to Example 18 (which also exhibitedR-3P)/Al=1.0).

The glass-ceramic of Example 21 included B₂O₃ and is believed to exhibitincreased indentation fracture resistance.

The precursor glass of Example 22 exhibited low liquidus viscosity (at1050° C.) and the resulting glass-ceramic exhibited an unabraded MOR ofgreater than about 3 GPa.

The glass-ceramic of Example 23 exhibited nepheline+Υ-eucryptite crystalphases. Without being bound by theory, it is believed that Example 23would exhibit a lower coefficient of thermal expansion (CTE).

The glass-ceramic of Example 25 is believed to exhibit increasedchemical durability due to the presence of NaCaPO₄ than Examplesincluding NaP.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention.

What is claimed is:
 1. A device comprising: a glass-ceramic articlecomprising; a major nepheline phase; and a minor phosphate phase,wherein the glass-ceramic article is colorless and has transmission orreflection color coordinates under the CIE L*, a*, b* colorimetry systemof L* in the range from about 80 to about 100, a* in the range fromabout −5 to about 5, and b* in the range from about b* in the range fromabout −5 to about 5, and exhibits a transmittance of about 70% orgreater across the visible spectrum, in the range from about 390 nm toabout 700 nm, wherein the device comprises any one of an electronicdevice, an automotive application, an architectural application and anenergy production application.
 2. The device of claim 1, wherein thedevice comprises an electronic device selected from the group consistingof: a mouse, a keyboard, a monitor, a tablet, a whitehoard, a personaldigital assistant, a navigation device an inventory device, a mediaplayer, an electronic reader, a mobile phone and a smart phone.
 3. Thedevice of claim 2, wherein the glass-ceramic article further comprises alithium aluminosilicate phase.
 4. The device of claim 2, wherein atleast one of the nepheline phase and the phosphate phase comprises aplurality of nanocrystals having a major cross-sectional dimension ofabout 100 nm or less.
 5. The device of claim 3, wherein a plurality ofnanocrystals form at least one of the nepheline phase, the phosphatephase and the lithium aluminosilicate phase, and the plurality ofnanocrystals have a major cross-sectional dimension of about 100 nm orless.
 6. The device of claim 5, wherein the plurality of nanocrystalsform the nepheline phase, the phosphate phase and the lithiumaluminosilicate phase.
 7. The device of claim 2, wherein theglass-ceramic article comprises a composition, the compositioncomprising, in mol %: SiO₂ in the range from about 35 to about 60, Al₂O₃in the range from about 10 to about 30, Na₂O in the range from about 7to about 31, K₂O in the range from about 0 to about 20, Li₂O in therange from about 0 to about 20, P₂O₅ in the range from about 1.5 toabout 8, and a rare earth oxide in the range from about 0 to about
 6. 8.The device of claim 7, wherein the composition further comprises atleast one oxide in an amount in the range from 0 mol % to about 8 mol %,wherein the at least one oxide comprises one of B₂O₃, MgO, CaO, SrO,BaO, and ZrO₂.
 9. The device of claim 2, wherein the glass-ceramicarticle further comprises a composition, the composition comprising, inmol %: SiO₂ in the range from about 40 to about 55, Al₂O₃ in the rangefrom about 14 to about 21, Na₂O in the range from about 13 to about 29,K₂O in the range from about 2 to about 14, Li₂O in the range from about0 to about 10, P₂O5 in the range from about 2.5 to about 5, and at leastone of ZrO₂, Y₂O₃ and La₂O₃ in an amount in the range from about 0 toabout
 4. 10. The device of claim 7, wherein the composition comprisesless than about 1 mol % TiO₂.
 11. The device of claim 2, wherein thenepheline phase comprises a solid solution.
 12. The device of claim 1,wherein the glass-ceramic article further comprises a compressive stresslayer, the compressive stress layer optionally comprising kalsilite. 13.The device of claim 1, wherein the glass-ceramic article furthercomprises an average surface compressive stress of about 400 MPa orgreater.
 14. The device of claim 2, wherein the glass-ceramic articlefurther comprises a compressive stress layer, the compressive stresslayer optionally comprising kalsilite.
 15. The device of claim 2,wherein the glass-ceramic article further comprises an average surfacecompressive stress of about 400 MPa or greater.